Conventional data backup techniques as applied to computing resources typically involve taking a periodic “snapshot” to preserve the state and data of computers and virtual machines that are hosted by computers. When taking a snapshot, it is typically necessary to first perform application quiescing to ensure data consistency. For example, in the case of a virtual machine running the Microsoft Windows™ operating system, application quiescing may be performed using the “Freeze” event handler of the Volume Shadow Copy Service (VSS). After the snapshot is taken, VSS may again be used to terminate the quiescence period using the “Thaw” VSS event handler. Likewise, the “Complete” VSS event handler may be used to cause data to be purged where such data are not required for future data backup operations, thereby freeing up system resources. In some virtual machine environments a software process on a virtual machine may receive instructions from outside of the virtual machine to initiate application quiescing, whereas once quiescence has been achieved instructions may no longer be received from outside of the virtual machine, such as to terminate the quiescence period or perform other post-snapshot operations. Such communications restrictions present a challenge to backup systems that operate separately from their data backup targets.